Isolated rat heart myocytes and the isolated perfused rat heart will be employed to study alpha receptor mediated effects of catecholamines on heart metabolism (amino acid transport; RNA and protein synthesis; glycogenolysis). Experimental variables include specific agonists (e.g., epinephrine, norepinephrine, phenylephrine, isoproterenol), specific antagonists (alpha vs beta), altered calcium flux (with calcium ionophores and transport blockers), altered thyroid status, and protein synthesis inhibitors.